Is it possible to limit the "Cycles Shadow from Transparency" per Object?
There will be a &quot;Transparent Shadows&quot; option per material in version 2.68 and the latest Blender builds.
Using a Light Path node to disable transparency helps and achieves the same visual result, but it still needs to execute the shader to find out, which costs some performance.
Update:
This is now accessible in materials &gt; settings: